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BUG: KCSAN: data-race in exit_signals / kthread_unpark

write to 0xffff8880b62fe024 of 4 bytes by task 19994 on cpu 0:
 exit_signals+0x13b/0x490 kernel/signal.c:2822
 do_exit+0x18b/0x18f0 kernel/exit.c:763
 kthread+0x17f/0x200 drivers/block/aoe/aoecmd.c:1242
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff8880b62fe024 of 4 bytes by task 20038 on cpu 1:
 to_kthread kernel/kthread.c:75 [inline]
 kthread_unpark+0x24/0xe0 kernel/kthread.c:474
 kthread_stop+0x97/0x2d0 kernel/kthread.c:557
 loop_unprepare_queue drivers/block/loop.c:883 [inline]
 __loop_clr_fd+0x3ad/0x720 drivers/block/loop.c:1145
 lo_release+0x153/0x160 drivers/block/loop.c:1817
 __blkdev_put+0x2cf/0x420 fs/block_dev.c:1867
 blkdev_put+0x89/0x2f0 fs/block_dev.c:1929
 kill_block_super+0x90/0xb0 fs/super.c:1445
 deactivate_locked_super+0x64/0xb0 fs/super.c:335
 deactivate_super fs/super.c:366 [inline]
 deactivate_super+0xca/0xe0 fs/super.c:362
 cleanup_mnt+0x27f/0x330 fs/namespace.c:1102
 __cleanup_mnt+0x1f/0x30 fs/namespace.c:1109
 task_work_run+0xf6/0x130 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x2b4/0x2c0 arch/x86/entry/common.c:163
 prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:274 [inline]
 do_syscall_64+0x353/0x370 arch/x86/entry/common.c:300
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 20038 Comm: syz-executor.1 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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